Ambient RF backscatter communication for vehicle remote control

ABSTRACT

A vehicle communicates with a remote key fob while ensuring an RF environment is sufficient to maintain adequate power from an RF-harvesting power supply that allows the fob to operate without a battery. The vehicle has a receiver adapted to detect a backscatter communication signal from the fob. A harvesting emulator in the vehicle is responsive to ambient RF around the vehicle to duplicate a concurrent response of the fob power supply. A vehicle-powered RF transmitter is activated to broadcast energizing RF radiation around the vehicle when the duplicated response is below a threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates in general to backscatter communicationperformed by a mobile unit powered by an RF harvesting power supply,and, more specifically, to vehicle communication for ensuring an RFenvironment sufficient to maintain adequate power from the RF harvestingpower supply.

Backscatter uses the reflection of incident radio signals as a means ofcommunication. Devices that backscatter RF generally require very littlepower (e.g., a few microwatts to tens of microwatts) and can actually bepowered by incident radio signals in the local RF environment (includingthe RF signal being backscatter and/or other incident RF radiation).This enables RF identification (RFID) tags that do not require abattery.

In some types of RFID systems employing backscatter, an active readertransmits a signal to a battery-less tag. Some tags may have thecapability to convert the frequency of the transmitted signal to adifferent backscattered frequency. The tag uses the energy of theincoming signal to power a controller that alternates an impedance of anantenna to modulate the signal and reflect the signal back with newinformation that can be decoded by the reader.

Passenger vehicles typically employ a remote keyless entry (RKE) systemwherein a wireless key fob carried by a user communicates with an RKEreceiver in the vehicle to provide remote user access to functions suchas locking and unlocking of doors and trunk, powered opening and closingof liftgates, car finder, panic alarm, activation of lights, and remoteengine start. Known key fobs employ active transmitters which requirebatteries. It would be desirable to eliminate batteries to provide moreconvenience to the user, improved structural robustness, and lower cost.

Key fobs may include devices carried by the vehicle user (e.g., in apocket or purse) as well as keypad units that are attached to thevehicle exterior which work via RF without direct connection to thevehicle electrical system. The invention also applies to other RFsignaling systems in a vehicle such as a tire pressure monitoring system(TPMS) or other sensors wherein sensor data is sent wirelessly from anelectrically isolated device to a receiver connected to the vehicleelectrical system. As used herein, the term fob includes both useractivated remote control devices and self-triggering wireless sensorswhich employ backscattering of RF to transmit commands and/or data.

RFID backscatter is the most common example of backscatter communicationin use today, but backscatter can be used with other RF protocols suchas Wi-Fi and Bluetooth® Low Energy (BLE). Since many vehicles arealready being manufactured with Wi-Fi and BLE systems, there exists thepotential to incorporate passive backscatter devices that can operatenear the vehicle by harvesting these (or other) RF signals and to usethe harvested energy to operate an antenna circuit to backscatter these(or other) RF signals to communicate with the vehicle to sendauthentication data and remote user commands, for example.

When using a vehicle-mounted transmitter to broadcast an RF signal thatpowers the remote device and that is then backscattered by the remotedevice, it would be necessary to continuously broadcast the RF while avehicle is parked. Otherwise, the RKE functions would not becontinuously available to the user. This would lead to high powerconsumption in the vehicle, potentially resulting in depletion of thevehicle battery to a point where engine starting could fail as well asreductions in the life of the battery. Another option would be for thekey fob to use ambient RF signals in the environment such as TV orcellular signals for deriving power and for modulated backscatteringthat could be sensed and decoded by the vehicle. However, sufficientambient RF is not always available, such as when the vehicle and key arein an underground parking structure or in a remote, rural area.

SUMMARY OF THE INVENTION

In order to provide continuous and reliable operation of a battery-less,backscattering key fob for communicating with a vehicle-mountedreceiver, an on-board tag having a substantially identical powerharvesting apparatus is used as a reference to evaluate an ability of anambient RF environment to provide sufficient power to operate the keyfob. Based on the evaluation by the on-board tag, the vehicle can powerup an RF source in the vehicle to broadcast an RF signal when necessaryfor use by the key fob. While the vehicle broadcasts the RF signal, itmay preferably continue to monitor for the appearance of sufficientambient RF from another source which would permit the turning off of thevehicle RF transmitter.

Adaptive control of the vehicle transmitter could be sensitive tointeraction with other vehicles also equipped with adaptive transmittersin ways that could disrupt availability or create excessive power drain.For example, if a vehicle is parked in a lot along with other similarlyequipped vehicles (e.g., at a manufacturing plant, vehicle dealershiplot, a place of business, or a shopping mall), in the event that theambient RF environment becomes too weak then many of the vehicles couldactivate their RF generators all at once. In view of the resulting surgeof RF, all the vehicles could then turn off their RF generators so thatthe environment again cannot support the backscatter units. The lack ofavailable RF energy would then lead to activation of RF generators in aplurality of the vehicles, and so on. To avoid such a counterproductiveloop, each transmitter can encode a tag within its transmitter RF signalto identify the vehicle and to coordinate operation of transmitters. Inone particular aspect of the invention, a vehicle comprises a receiveradapted to detect a backscatter communication signal from a wireless fobpowered by an RF-harvesting power supply in the fob. A harvestingemulator in the vehicle is responsive to ambient RF around the vehicleto duplicate a concurrent response of the fob power supply. Avehicle-powered RF transmitter is activated to broadcast energizing RFradiation around the vehicle when the duplicated response is below athreshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one type of prior art backscattercommunication system.

FIG. 2 is a block diagram showing a vehicle communication system using amobile key fob with RF power harvesting in a remote keyless entrysystem.

FIG. 3 is a block diagram of one preferred embodiment of the inventionusing an on-board power harvesting emulator.

FIG. 4 is a flowchart showing one preferred method of the invention thatcan be practiced using the apparatus of FIG. 3.

FIG. 5 is a diagram showing several vehicles in close proximity having apotential for undesirable interaction between RF transmitters.

FIG. 6 is a block diagram showing vehicle transceivers for coordinatingoperation of energizing RF broadcasts among the receivers of FIG. 5.

FIG. 7 is a block diagram showing a mobile unit responsive to multipleRF bands.

FIG. 8 is a flowchart showing a method for operating a vehicle apparatusto interact with the mobile unit of FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a backscattering device 10 as known in the priorart is shown for communicating with a receiver 11 by backscatteringambient RF signals. A broadcast source 12 can include many types oftransmission such as television, cellular, AM or FM radio, Wi-Fi, andBluetooth signals. Ambient RF signals 13 from source 12 contribute to anRF environment in the vicinity of backscatter device 10 and receiver 11.

Device 10 has an antenna 14 for receiving ambient RF signals 13 which isconnected in series with a transistor 15 which acts as a controllableload in series with antenna 14 to selectively generate a backscatter RFsignal 16 that propagates to receiver 11. By turning the backscatteringfunction on and off, device 10 encodes the RF signal with a desired datasignal which can be differentiated from the direct broadcast of RFsignal 13 by receiver 11 using various techniques known in the art.

In order to provide batteryless operation, device 10 includes a powerharvesting circuit 17 connected with antenna 14. RF energy from antenna14 may be rectified and stored for supplying various electroniccomponents 18 using techniques known in the art. The harvesting mayinclude the RF signal to be backscattered as well as other RF sourceswithin the RF environment acting upon antenna 14. In addition, otherantennae can be provided for harvesting RF sources in other portions ofthe RF spectrum. The powered electrical components include a controlblock 20, data memory 21, an encoder 22, and input/output (I/O)components 23. RF backscatter devices have been used for many differentapplications such as RF tagging systems, remote sensors, and remotecontrols. Data 21 may include identification data, and I/O block 23 mayinclude sensors such as touch-sensitive switches for manually triggeringvarious user commands to be transmitted by forming command data incontrol block 20 and then encoding the data in encoder 22 for drivingtransistor 15 with the encoded data.

In a backscatter system similar to FIG. 1, receiver 11 can alsoincorporate a broadcast RF source to energize device 10 and to providean RF signal suitable for being backscattered. Depending on the type ofsystem being implemented, receiver 11 can be an actively powered deviceor can also be batteryless. When being used in a passenger vehicle,receiver 11 may typically obtain power from a vehicle battery. Inbatteryless embodiments, receiver 11 could be another backscatteringdevice such as another remote control device or an RFID tag.

As shown in FIG. 2, backscatter device 10 may be utilized in connectionwith a remote keyless entry system in a vehicle 25. An RKE controller 26includes an antenna 27 for receiving backscattered signals from device10 in order to control various vehicle components such as door locks 28or the starting of an internal combustion engine 29, for example.However, since vehicle 25 may be parked in various remote or RF shieldedlocations, the presence of sufficient ambient RF signals in theenvironment around device 10 for providing sufficient energy forharvesting and for backscattering cannot be guaranteed under allcircumstances.

In order to ensure continuously available RF energizing signals and asignal appropriate for backscattering for use in a vehicle remote entrysystem, an embodiment is shown in FIG. 3 which includes a backscatteringdevice 30 for communicating with a vehicle 31. When available, RFsignals from an ambient broadcast source 32 (such as TV, cellular, andWi-Fi broadcast signals) may be relied upon so that power from a vehiclebattery (not shown) is conserved. Backscattering device 30 preferablycomprises a wireless key fob with a power harvesting circuit 33connected to an antenna 34 which is connected in series with atransistor switch 35. When sufficient power is being generated byharvesting circuit 33, then a transmitter 36 can respond to sensors 37which sense manual activations by a user in order to trigger thetransmission of authentication and command signals to vehicle 31 bymodulating backscattering by antenna 34 via transitions of transistor 35to produce a backscattered signal 38.

In order to determine whether an RF environment at the location ofvehicle 31 and key fob 30 is adequate to provide reliable communicationusing ambient signals alone, a power harvesting emulator 40 with anantenna 41 is provided in vehicle 31 which is responsive to the ambientRF around vehicle 31 such that it duplicates an RF response which isconcurrently occurring in the power harvesting circuit 33 of key fob 30.For example, emulator 40 may include a power harvesting circuit andantenna mounted in vehicle 31 which are substantially identical to thosein key fob 30 (emulator 40 should be placed in an arrangement thatprovides equal sensitivity to the ambient RF environment). The output ofemulator 40 (e.g., a measured power level) may be compared with athreshold T by a comparator 42, and the result of the comparison isprovided to an RF generator 43 which can output a broadcast signal to atransmit antenna 44. More specifically, when the duplicated response ofemulator 40 is below the threshold then RF generator 43 is activated tobroadcast an energizing RF radiation signal 45 which propagates to keyfob 30. Otherwise, RF generator 43 is deactivated. Energizing radiationsignal 45 is adapted to couple with antenna 34 and to provide sufficientpower to support harvesting within circuit 33. Furthermore, RF radiation45 is adapted for backscattering by key fob 30 so that backscattered RFsignal 38 can be detected and demodulated by a receiver 46 and antenna47. Although shown separately, RF generator 43 and receiver 46 can becombined into a single transceiver.

Although energizing RF radiation signal 45 can coincide with thebackscattered signal to be detected by receiver 46, the backscatteringcommunication could alternatively be conducted using another RF signalthat is present (e.g., in a different frequency spectrum) while signal45 is only used for harvesting power. As explained later in connectionwith FIGS. 7 and 8, a receiver and multiband antennae can be includedwithin key fob 30 so that two-way communication can be conducted toallow key fob 30 and vehicle 31 to agree upon a frequency band to bebackscattered.

One preferred method of the invention is shown in FIG. 4 wherein theon-board emulator harvests the ambient RF environment to generate powerat a level that duplicates (i.e., estimates) the power level beingconcurrently harvested within the key fob in step 50. In step 51, acheck is performed to determine whether the duplicated response isgreater than the threshold. The threshold can be set in such a way thatthe distance between the vehicle and the fob can be estimated and thesignal loss between the vehicle and key fob is assumed as the signaldegrades with distance. If greater than the threshold, then a return ismade to step 50 for continued monitoring of the ambient RF environment.If the power is not enough, then the RF generator is turned on in step52.

Whenever it is available (e.g., when a user manually activates an inputswitch), backscatter data is detected in step 53 by the on boardreceiver. In an optional embodiment having two-way communication, theenergizing RF radiation from the RF generator can be modulated in step54 in order to transmit commands to a key fob with an optional receiverfor detecting and demodulating the commands. For example, the key fobmay optionally include a receiver circuit that responds to variations inthe energizing RF radiation (e.g., a pulse-encoded data signal) forimplementing various actions such as setting a backscatter frequency asdescribed in detail more detail below. As used herein, the RF generatorcan be comprised of any RF transmitting device in the vehicle and doesnot require a standalone unit. In step 55, the ambient RF environment isperiodically resampled and compared in step 56 to the power threshold sothat if an ambient RF broadcast source or other nearby sources becomepresent then the RF generator can be turned off, and then a return ismade to step 50.

Use of an onboard RF transmitter over significant periods of time with avehicle being parked can lead to excessive battery drain especially insome particular situations. For example, FIG. 5 depicts a situationwherein vehicle 31 and other vehicles 57 and 58 are parked in a commonarea 59 such as a parking lot, resulting in the vehicles all beingwithin a maximum operating range of the backscatter communicationsystem. At an initial time to, there is no ambient RF broadcastingsignal entering the RF environment which is sufficient to support RFharvesting and/or backscattering. The absence of sufficient ambient RFwould be detected in vehicles 31, 57, and 58, causing each of them toturn on their RF generator at a time t₁. However, each vehicle thendetects the RF being broadcast by the other vehicles. Consequently, allthe vehicles may then simultaneously turn off their RF generators at atime t₂. A resulting oscillation of the RF generators between their onand off states will fail to enable backscatter communication and willcause excess power drain in the batteries of all the vehicles.

FIG. 6 shows an embodiment wherein several different alternativemodifications can be made to prevent oscillation of the generatorsand/or to improve sharing of the RF broadcasting function betweendifferent vehicles in a way that minimizes power drain. In particular, avehicle 60 is adapted to interact with a second vehicle 61 in a way thatprevents erroneous activation/deactivation cycles of the generators. Inan extended embodiment, vehicle interactions can distribute energyconsumption among the vehicles in an optimized manner. Relevantcircuitry in vehicles 60 and 61 may be identical, but FIG. 6 showsselected details within each vehicle to describe the associatedcommunication functions from the perspective of vehicle 60.

A backscatter communication system 62 in vehicle 60 includes a carriergenerator 63 under control of a power supply switch 64. In oneembodiment, a logic block 65 could force a Mode signal to assume an offstate based on a manual input indicating that the RKE system should notbe operational (such as when the vehicle is at the manufacturing plantor being transported to a dealership). With switch 64 turned off, thecarrier generator lacks power to operate.

In another embodiment in which RF generator operation can be coordinatedbetween a nearby vehicle, logic circuit 65 determines the Mode signalusing additional information to control the gate of switch 64 toselectably activate the RF generator function. A carrier signal fromcarrier block 63 is modulated in a multiplier 67 according to anidentification tag 66 before being radiated as an energizing signal 70from an antenna 68. In vehicle 61, an antenna 71 receives energizingsignal 70 and a power harvesting emulator 72 harvests the signal onantenna 71 to generate a DC output. A measured power of the DC output iscompared to a threshold in a comparator 73 having its output connectedto one input of an AND gate 74. A tag detector 75 is connected toantenna 71 in order to detect identification tag 66 which has beenencoded in energizing signal 70. Tag detector 75 is further adapted tocharacterize or classifying the detected tag according to whether thepresence of vehicle 60 should impact operation of the RF generatorfunction of vehicle 61. For example, identification tags may identifyvehicles as being of a common design (e.g., made by the same vehiclemanufacturer). This may indicate common/compatible backscattering systemmaking it unnecessary for both vehicles to be broadcasting energizing RFsimultaneously. If tag detector 75 determined that it should not operateits RF generator because vehicle 60 is already broadcasting, then anoutput signal from detector 75 which is coupled to an inverting input ofAND gate 74 ensures that a mode signal within vehicle 61 is set to anoff state.

In another embodiment, optimal assignment of vehicles for operatingtheir RF generator can be obtained using an RF transceiver 76 withantenna 77 (which would be duplicated in all cooperating vehicles). Amoderator circuit 78 may be programed to arbitrate between variousvehicles based upon a state of charge (SOC) of each respective vehiclebattery or other factors. For example, moderator circuits in thevehicles can agree to cycle between respective vehicles forpredetermined periods of time in order to share the power consumptionamong vehicles. For example, RF transceiver 76 in vehicle 60 transmitsits identifying tag via RF transceiver 76 (and/or within RF energizingsignal 70) in order to identity itself to nearby vehicles. RFtransceiver 76 simultaneously detects ancillary ID tags being broadcastby other vehicles (within dedicated communication links or usingrespective energizing RF radiation signals), so that a group of vehiclescan be identified/tracked which are adapted to cooperate with each otherand to arbitrate among them which RF generator will operate at any onetime.

In order to avoid depletion of the state of charge of a main battery ofa vehicle to a level where critical functions (such as engine starting)cannot be performed, SOC monitoring can be used even when coordinationbetween nearby vehicles is not being employed. For example, the batterySOC can be compared to an power-reserve threshold, and when the measuredSOC is below the power-reserve threshold then activation of the RFgenerator could be inhibited. This may force the user to obtain entry tothe vehicle using means other than the backscatter system (e.g., use ofa mechanical key or a vehicle-mounted keypad).

FIG. 7 shows another embodiment wherein a backscatter device 80 providesmultiband operation using a first antenna 81 and a second antenna 82. Insome embodiments, a single antenna can alternatively be used toreceive/transmit on multiple bands simultaneously. Both antennae 81 and82 are connected to power harvesting circuit 83. An antenna 79 may alsobe connected to power harvesting circuit 83 which is dedicated for onlycollecting energy within a respective frequency band if desired. Byharvesting power from a plurality of different frequency bandssimultaneously, the likelihood of providing sufficient harvested poweris increased.

An encoder 84 may be connected to transistors 85 and 86 connected inseries with antennae 81 and 82, respectively. Encoder 84 can drive justone or both transistors 85 and 86 depending on whether it is desired tobackscatter ambient signals within each respective frequency band.

In order to allow a vehicle transceiver to set a backscatter frequencyband to be used, a receiver 87 is included which is connected withantenna 81, whereby command signals from the vehicle transceiver can bereceived. A dedicated frequency or channel could be used fortransmitting the commands (e.g., using the frequency band received byantenna 81). Command signals are decoded in receiver 87 and provided toa control logic block 88 which controls encoder 84. As in the previousembodiment, input/output components 89 can also be connected to controllogic block 88 for inputting user commands to the key fob.

FIG. 8 shows a preferred method using the multiband capabilities of thebackscatter device in FIG. 7. Thus, power is harvested within multiplebands in step 90. A substantially identical power harvesting emulatorwithin the vehicle performs a check in step 91 to determine whethersufficient power is available in the multiple bands. If not, then the RFgenerator is turned on in step 92. In step 93, the vehicle mountedtransceiver identifies frequency bands which contain available ambientRF signals that are appropriate for backscattering. In the event thattwo-way communication is not being used, then the vehicle receiver canmonitor all suitable RF signals in step 94 (e.g., allowing the key fobto select an antenna to be modulated). When two-way communication isavailable, then the vehicle apparatus may apply ranking criteria in step95 among all available RF signals to select the most desirable signalfor backscattering. Then, the vehicle transceiver transmits a frequencycommand to the fob in step 96 and communication proceeds with theselected frequency band.

What is claimed is:
 1. A communication system for a vehicle comprising:a wireless fob carried outside the vehicle comprising an RF-harvestingpower supply responsive to ambient RF signals, and comprising aswitchable antenna generating a backscatter communication signal; areceiver in the vehicle adapted to detect the backscatter communicationsignal from the wireless fob; a harvesting emulator in the vehicleresponsive to the ambient RF signals to duplicate a concurrent responsepresent in the RF-harvesting power supply of the wireless fob; and avehicle-powered RF transmitter in the vehicle activated to broadcastenergizing RF radiation around the vehicle when the duplicated responseis below a threshold.
 2. The communication system of claim 1 wherein thereceiver detects backscatter of the energizing RF radiation to receivethe backscatter communication signal.
 3. The communication system ofclaim 1 wherein the receiver detects backscatter of an ambient broadcastsignal other than the energizing RF radiation.
 4. The communicationsystem of claim 1 wherein the RF transmitter modulates the energizing RFradiation to convey a command signal to the fob.
 5. The communicationsystem of claim 4 wherein the command signal identifies a frequency bandto be backscattered by the fob.
 6. The communication system of claim 1wherein the receiver is comprised of a transceiver adapted to i)modulate the energizing RF radiation according to an identifying tag,and ii) detect ancillary tags broadcast by other vehicles withinrespective energizing RF radiation of the other vehicles; whereinactivation of the vehicle-powered RF transmitter further depends onancillary tags being received.
 7. The communication system of claim 6wherein ancillary tags are adapted to identify a group of cooperatingvehicles to which the vehicle belongs, and when a detected tagidentifies the group then the vehicle-powered RF transmitter is notactivated.
 8. The communication system of claim 6 further comprising amoderator adapted to communicate with moderators in the other vehiclesto cooperatively assign respective vehicle-powered RF transmitters forbroadcasting the energizing RF radiation one at a time.
 9. Thecommunication system of claim 8 wherein an assigned transmitter isdetermined in response to a highest one of respective states of chargeof respective storage batteries in the vehicles.
 10. The communicationsystem of claim 8 wherein an assigned transmitter is determined bycycling between respective vehicles for predetermined periods of time inorder to share a power consumption among the respective vehicles. 11.The communication system of claim 1 wherein activation of thevehicle-powered RF transmitter is prevented when a state of charge of astorage battery in the vehicle is below a power-reserve threshold.
 12. Avehicular communication method comprising: operating a backscatter fobto generate a backscatter communication signal using power harvestedfrom a local RF environment including ambient RF signals, wherein thebackscatter fob is a portable device carried outside a vehicle;emulating the power harvesting of the fob in a vehicle mounted emulatorreceiving the ambient RF signals to provide a measured power; andactivating a vehicle-powered transmitter to boost the local RFenvironment when the measured power is below a threshold to increase thepower harvested in the fob.
 13. The method of claim 12 wherein the fobis comprised of a key fob, the method further comprising: detectingbackscatter by the key fob of an RF signal transmitted by thevehicle-powered transmitter to boost the local RF environment; anddemodulating the detected backscatter to recover authentication data anduser commands manually selected at the key fob.
 14. The method of claim12 wherein the fob is comprised of a key fob, the method furthercomprising: detecting backscatter by the key fob of an ambient RF signalfrom a remote broadcaster to the local RF environment; and demodulatingthe detected backscatter to recover authentication data and usercommands manually selected at the key fob.
 15. The method of claim 12wherein the step of activating the vehicle-powered transmitter includesmodulating an RF signal transmitted by the vehicle-powered transmitterto boost the local RF environment in order to convey command signalsfrom the transmitter to the fob.
 16. The method of claim 15 wherein theconveyed command signals identify a frequency band to be backscatteredby the fob.
 17. The method of claim 12 further comprising: using RFcommunication tags within RF signals transmitted by a plurality ofvehicle-powered transmitters of respective nearby vehicles in order totrack the vehicles; and coordinating operation of the transmitters ofrespective vehicles to distribute an energy consumption among thevehicles.
 18. The method of claim 17 wherein the coordinating stepdetermines a vehicle with a highest state of charge of a respectivestorage battery that powers a respective transmitter and assigns thedetermined vehicle to exclusively transmit the RF signal for boostingthe local RF environment.
 19. The method of claim 17 wherein thecoordinating step cyclically assigns respective vehicles forpredetermined periods of time in order to share a power consumptionamong the respective vehicles.
 20. A vehicle comprising: a receiveradapted to detect a backscatter communication signal from a wireless fobpowered by an RF-harvesting power supply; a harvesting emulatorresponsive to ambient RF around the vehicle to duplicate a concurrentresponse of the fob power supply; and a vehicle-powered RF transmitteractivated to broadcast energizing RF radiation around the vehicle whenthe duplicated response is below a threshold; wherein the harvestingemulator periodically re-samples the ambient RF during activation of theRF transmitter to update the duplicated concurrent response unaffectedby the energizing RF radiation.